Why You Should Secretly Hope for a Thumbsucker or Nail-Biter

Most parents are aware of the idea that a childhood absent of germs could set kids up for miserable allergies later in life. It's known as "hygiene theory," and it's what makes the fact that your child is eating crackers off the floor or licking the bottom of a shoe almost tolerable.

A new study has brought even better news for parents of kids whose fingers are always in their mouths. Thumbsuckers and nail-biters are engaging in a habit that is paying off big time in the future in the form of fewer allergies.

A study in the August journal of Pediatrics, availabe online now, found that exposure to microbial organisms among thumbsuckers and nail-biters ages 5 to 11 were significantly less likely to have common skin allergies as adults.

The study, “Thumb-Sucking, Nail-Biting and Atopic Sensitization, Asthma and Hay Fever,” by researchers at the University of Otago in Dunedin, New Zealand, followed 1,037 participants born in 1972-1973. Parents reported childrens thumbsucking and nail-biting habits when their kids were 5, 7, 9 and 11. Researchers then checked the kids at 13 and 32 years for "atopic sensitization," which is when a skin prick test of a common allergen shows up positive.

In those teen years, 38 percent of the study's participants who sucked their thumbs or bit their nails tested positive for allergies. Among those who had not developed those habits, the positive tests came in at 49 percent. Those who both sucked and bit? They're the real beneficiaries. The study found positive allergy tests in just 31 percent of them.

Photograph by Twenty20

"The associations were still present at age 32 years and persisted even with adjustments for confounding factors such as sex, parental history of allergies, pet ownership, breast-feeding and parental smoking," the American Association of Pediatrics reported on the study.

Prof Malcolm Sears, from McMaster University in Canada, said the findings are consistent with “hygiene theory,” the UK Telegraph reported, but stopped short of saying parents should encourage these habits.

Also important to keep in mind: While these habits lowered rates of allergies to peanuts and all that, they had no apparent effect on the rates of asthma or hay fever.